Thixoforming : Semi-solid Metal Processing

4.8 Recycling of Aluminium–Lithium Alloys from Thixoforming Processesj141
Figure 4.28 Calculated Li yield of Al–Li alloys at 750 C after
contact with NaCl–KCl–LiCl depending on the LiCl content of the
salt mixture.
As an example, Figure 4.29 shows that during treatment of an AlLi2.5Mg4 metal
melt using 70NaCl–20KCl–10MgCl2 molten salts, Li was completely transformed by
MgCl 2 into LiCl (see Section 4.7.2). The equilibrium is attained in this case after
a short period of 3–4 min. Also for the treatment of AlLi4Mg8 alloy using
70NaCl–27KCl–3LiF molten salts, the Li is completely transformed by the NaCl
into LiCl and a small amount of Mg by LiF into MgF2. The experimental testing in its
entirety largely confirms the thermochemical calculations. The use of an NaCl–KCl
salt mixture with additives of LiF, CaF2 or MgCl2 leads to transfer of the Li from the
metal alloy into the molten salts. When using MgCl2 as an additive, the Mg content
increases in correspondence with the transfer of Li into the molten salts, which could
partially be compensated for by the addition of LiF. By the addition of CaF 2 a
transformation of Mg into the molten salts is achieved, and also that of the Li. As
calculated in Section 4.7.2, the lithium is nearly completely transferred to the molten
salts (residual content in the metal melt